In the isostatic pressing of articles a powdered material is generally placed within a deformable mold, for example a mold constructed of polymeric material such as rubber or polyurethane. The mold is then placed within a canister, which is usually perforated, and the canister is then placed within an isostatic press and subjected to elevated pressures.
Although articles of many shapes can be formed by isostatic pressing, problems are presented when it is desired to produce long, slender rods. Exemplary of such problems are the events which lead to the making of the invention disclosed herein. Thus, attempts were made to isostaticly mold slender rods by the following procedure. Powdered tungsten material was packed in a latex mold 600 mm in length and having an internal diameter of 19 mm and a wall thickness of 1.5 mm. The rubber mold was then sealed and placed in a conventional, perforated canister. FIGS. 1 and 2 show the arrangement which resulted.
More specifically, as shown in FIGS. 1 and 2, the arrangement included a perforated steel canister 10 surrounding the latex mold 12 which contained the tungsten powder 14. In accordance with conventional practice, the mold 12 was sealed with a latex plug 18 and a rubber seal ring 20 which compressed the mold against a steel ring 24.
Canister arrangements of the type shown in FIG. 1 were isostaticly pressed at pressures of 45,000 psi or 60,000 psi. After each was removed from the press it was found that the mold was stuck within the canister. Upon close inspection of the mold and canister, it appeared that certain parts of the mold were secured to the formed rod and between the points of securement bubbles had formed and the bubbled portions of the mold were jammed against the canister. FIG. 3 suggests the arrangement of the rod, mold and canister which was generally found to exist wherein, at points 22, the mold 12 was secured to the rod 14 and therebetween bubbles 34 had formed in the mold and were jammed against the canister 10. To remove the mold from the canister, it was necessary to puncture each of the balloons with a needle.
After each of the molds was removed from its respective canister, substantial difficulty was encountered in the removal of the rod from the mold. In certain cases, it was possible to remove the rod from the mold by inserting the mold in a vacuum chamber. In most cases, however, it was found that the compacted rod was broken in two or three location, as shown at 39 in FIG. 3, before the mold was removed. Typically, out of twenty pressings only four complete rods would be obtained.
After a number of unsuccessful attempts, urethane molds were tried in place of the latex rubber molds. For these tests, both hard and soft urethane material was employed and with molds having both thin and thick walls. With each of these tests it was found that the compacted rod was broken into more than ten pieces.
Subsequently, it was attempted to mold slender rods through the use of an unperforated canister. However, again it was found that bubbles were formed and the mold could only be removed after puncturing the bubbles with a needle and, even with this procedure, a majority of the rods were found to be broken after removal from the mold.
The invention disclosed herein provides a simple solution of the problem of isostatically molding slender rods.